Various chemicals are released in our environment as herbicides/pesticides, degreasers, fire retardants, industrial solvents o as by-products of chemical industry, leading to major environmental pollution problem. The U.S. Congress specifically authorized the Super Funds to clean up thousands of toxic dump sites in the United States, but very few have been cleaned up. Microorganisms are responsible for recycling natural wastes, but they are relatively inert towards synthetic compounds, particularly the high chlorinated compounds that occur rarely in the natural environment. Yet, microorganisms are highly adaptable and have evolved, and are continually evolving, the genes, both structural and regulatory, that specify biodegradation of a variety of simple chlorinated compounds. Microbial remediation of highly chlorinated compounds is thus a major goal to address problems of toxic chemical pollution. To accelerate the rate of microbial biodegradation of a toxic, synthetic chemical, one needs to understand the nature of regulation of the structural genes, and the mechanism of action as well as evolution of such regulatory genes. However, even when a microorganism becomes available for effective degradation and removal of a toxic chemical, it cannot necessarily be used in bioremediation unless its pathogenic potential to local populations has been determined. This proposal has two major goals. The first to understand how degradative pathways for simple, as well as somewhat recalcitrant, chlorinated compounds evolve in nature. We are particularly interested in the evolution and the mode of action of regulatory genes that regulate the level of expression of the structural genes in the biodegradative pathway. Our second goal is to develop both conceptual and technical understanding and approaches to assess the pathogenic potential of a bioremediating organism. The progress achieved and the ways we intend to meet our goals are detailed in this proposal